Axle width/tire question

[jelfert]

I have a 1958 fleetside that I want to mount some MT sportsman radial 29X18.00R 15 tires on the rear. I have the stock frame width. I'm sure a few of you on here have mouonted these tires on your trucks. What axle width, brakes and wheel backspace did you use? I will be using willwood disc brake conversion. The plan is to have the axle built (4 link) with the brakes installed and shipped to me so I want to get it right the first time!